#给定两个字符串形式的非负整数 num1 和num2 ，计算它们的和并同样以字符串形式返回。
class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        n, m = len(num1), len(num2)
        a = b = 0
        for i in range(0,n):
            a = a + pow(10,n-1-i) * (ord(num1[i]) - 48)
        for j in range(0,m):
            b = b + pow(10,m-1-j) * (ord(num2[j]) - 48)
        c = a + b
        return str(c)